1. Field of the Invention
The present invention relates to a technology for supplying power necessary for driving a panel of a liquid crystal display device, and more particularly, to a power supply circuit of a liquid crystal display device, which can suppress electromagnetic interference (EMI) by using charging control signals and loading control signals periodically or irregularly changed when a gate voltage is generated.
2. Description of the Related Art
FIG. 1 is a schematic block diagram illustrating a conventional liquid crystal display device. Referring to FIG. 1, the liquid crystal display device includes a liquid crystal panel 110, in which a plurality of gate lines and a plurality of data lines are arranged while being cross each other to define a plurality of pixel areas in a matrix shape, and an LDI driver IC 120. The LDI driver IC 120 includes a driving circuit unit 121 that supplies the liquid crystal panel 110 with a driving signal and a data signal, and a power supply 122 that supplies power necessary for the driving circuit unit 121.
The driving circuit unit 121 includes a gate driver 121A, a source driver 121B, and a timing controller 121C.
The gate driver 121A outputs a gate driving signal for driving each gate line of the liquid crystal panel 110.
The source driver 121B outputs a data signal to each data line of the liquid crystal panel 110.
The timing controller 121C controls the driving of the power supply 122 as well as the driving of the gate driver 121A and the source driver 121B.
The power supply 122 includes a power controller 122A, a source power driver 122B, and a gate power driver 122C.
The power controller 122A controls the driving of the source power driver 122B and the gate power driver 122C under the control of the timing controller 121C.
The gate power driver 122C generates and supplies a gate high voltage VGH and a gate low voltage VGL, which are required when the gate driver 121A generates the gate driving signal.
A power supply circuit provided in the gate power driver always outputs a switching pulse with the same phase as illustrated in FIG. 2A when outputting charging control signals and loading control signals for generating the gate high voltage VGH and the gate low voltage VGL. Therefore, the spectrum is concentrated at a band around the center frequency fo as illustrated in FIG. 2B.
The source power driver 122B supplies panel driving voltages VDDP and VDDN with positive and negative polarities, which are required when the source driver 121B generates the data signal.
As described above, the power supply circuit provided in the gate power driver outputs the charging control signals and the loading control signals with fixed phases in order to generate the high gate voltage and the low gate voltage, thereby causing severe electromagnetic interference (EMI).
Furthermore, since charging control signals and loading control signals with different phases are used whenever a new frame starts, an image may be unstably displayed.